LED (light emitting diode) drive units for driving a plurality of serially-connected LEDs have conventionally been known (see, for example, Patent Document 1). Backlight units provided with, for example, such LED drive units have also been conventionally known.
FIG. 9 is a plan view schematically showing an example of the structure of a conventional backlight unit. FIG. 10 is a diagram for illustrating the structure of a light source of the conventional backlight unit shown in FIG. 9. FIG. 11 is a diagram for illustrating the structure of a lighting circuit connected to the light source of the conventional backlight unit shown in FIG. 9. First, with reference to FIGS. 9 to 11, a description will be given of an example of the structure of a conventional backlight unit.
In the conventional backlight unit 110, as shown in FIG. 9, a light guide plate 101, a light source (a plurality of LEDs 102), and the like are accommodated inside a backlight frame 103. Although not illustrated, a reflection sheet and an optical sheet are also accommodated inside the backlight frame 103.
The plurality of LEDs 102 forming the light source are mounted on a given substrate 104. Furthermore, the plurality of LEDs 102 are arranged at predetermined intervals in a direction (direction A) along a light entrance surface 101a of the light guide plate 101 such that each of the LEDs 102 faces the light entrance surface 101a of the light guide plate 101.
As shown in FIG. 10, as well as being serially connected, the plurality of LEDs 102 are structured such that they emit light by being fed with a drive current from the lighting circuit 120. The lighting circuit 120 feeding the plurality of LEDs 102 with a drive current, as shown in FIG. 11, has one constant current circuit portion 121 and one light control portion 122. The constant current circuit portion 121 has a function of generating a predetermined constant current. The light control portion 122 has a function of regulating the amount of drive current fed to the plurality of LEDs 102 (see FIG. 10) according to a light control signal fed from outside.
Lower-brightness lighting operation can be performed with the above-described conventional backlight unit 110 than with a conventional backlight unit using a CCFT (cold cathode fluorescent tube) as the light source. Incidentally, the LEDs 102 emit light with a current equal to or less than a several percent (for example, approximately 1%) of a rated current.
Patent Document 1: JP-A-2007-42758